1. Field of the Invention
The present invention relates to a construction of a supporting shaft for supporting a roll of paper.
2. Description of the Prior Art
Some types of image forming apparatus, such as copying machines, various kinds of printers and the like employ, a long length of paper rolled around a core cylinder, that is a so-called roll of paper or paper roll. A known supporting shaft 99 for supporting this roll of paper touches internally an inner circumferential surface S of a core cylinder 96 of the roll of paper at three points as seen in the direction of a longitudinal axis, as shown in FIG. 15 and FIG. 16. Such supporting shaft includes a supporting member 91 having a first supporting element (d) and a second supporting element (e) and two flat plate members 92 fixedly mounted on a spindle or core shaft 93. An arm 95 extending in the direction of the axis of core shaft 93 is pivoted by a supporting shaft 94 extending orthogonal to such axis to midway portions in the longitudinal direction of flat plate members 92. A saw-toothed third supporting element (f) located adjacent shaft 94 is located on arm 95. Energizing means 97 urges arm 95 and thereby third supporting piece (f) against the inner circumferential surface S of core cylinder 96. Reference numeral 98 designates a balancer.
With the above described construction, paper roll supporting shaft 99 can be inserted into and drawn out the core cylinder 96 by moving the arm 95 toward the core shaft 93 against the force of energizing means 97.
Also known is a construction in which the above described arm 95 is omitted and outer end edges of the flat plate members 92 are used as the third supporting element so that such end edges may be engaged with inner circumferential surface S of core cylinder 96. In such case, the core cylinder is supported at substantially three points by pushing the supporting shaft into the core cylinder.
However, in all of the above described constructions, the number of parts and assembly time required are increased, and also the weight of the overall structure is increased. In particular, the core shaft 93 is heavy and it is necessary to reduce the weight thereof.
Separately from the above described problems, a disadvantage of such known construction is that the position of contact of third supporting element (f) with surface S limited and occurs only in the vicinity at which the arm 95 is pivoted. Thus, opposite longitudinal ends of the core cylinder 96 are not supported by third supporting element (f) and are apt to be swung in radial directions about the third supporting element (f) as a fulcrum. As a result, drawing out and supply of paper from the paper roll will not be stable and thus poor paper supply, such as an oblique paper supply, is apt to occur.